* Water leak suggests faster than usual corrosion and damage
* Japan's biggest nuclear reactor shut since May 2011
* Company will have to keep buying oil and gas to make up
By Risa Maeda
TOKYO, Aug 2 Chubu Electric Power Co
could face the prospect of decommissioning Japan's biggest
nuclear reactor after assessing damage this month from the
world's first known case of seawater infiltration of a reactor
More than a year after the firm's Hamaoka nuclear plant was
shut for safety reasons following the Fukushima disaster, water
contaminated with low-level radiation is seeping internally in
the No.5 unit's turbine building, suggesting serious damage to
the core, experts said.
"We have not decided if the unit is to be decommissioned or
whether the unit will be operable after repairs. We're making
assessments in order to make a decision," Chubu Electric
spokesman Akio Miyazaki said on Thursday.
A decommissioning or prolonged shutdown for repairs means
Chubu Electric, which has reported four consecutive quarters of
losses since Hamaoka was idled, will have to keep tapping oil
and gas markets to run fossil-fuel stations, adding to the woes
of Japan's third-biggest utility.
Reuters calculations show the company may have to import an
extra 5 million tonnes of liquefied natural gas for each year
the 3,617-megawatt Hamaoka plant is closed, assuming the
generation shortfall is solely met by gas-fired plants.
Seawater entered the No.5 unit when Chubu Electric was
shutting Hamaoka in May last year on orders from then-Prime
Minister Naoto Kan because of concerns a large earthquake might
strike nearby, producing a tsunami that would overwhelm the
plant, as in the Fukushima disaster two months earlier.
As the shutdown of the seven-year-old unit with a capacity
of 1,380 MW started, saltwater used for cooling steam from the
boiling water reactor entered t h e core after a burst pipe
damaged one of its heat exchangers.
About 400,000 litres (88,000 gallons) of corrosion-causing
sea water entered the turbine building, with 5,000 litres
getting into the reactor itself.
The extremely rare event set off an investigation that has
unearthed widespread corrosion in the labyrinth of piping, pumps
and steel partitions in the reactor building and secondary
As recently as Monday, the utility said it found water
contaminated with low levels of radiation in the turbine
building adjacent to Hamaoka's No.5 reactor.
"More detailed data from the operator is needed to make a
judgement. But we should assume the reactor's strength has been
impaired," said Atsushi Kasai, a former technical advisor on
nuclear power to Shizuoka prefecture, where Hamaoka is located
about 200 kilometres (120 miles) southwest of Tokyo.
Chubu Electric says no radiation has leaked to the
environment but the discovery of radioactive cobalt below a
13-meter-high cooling tank beside the reactor confirms unusually
fast corrosion through the walls of the stainless-steel tank.
As reactors abroad mostly use river water to cool the steam
turbines used for power generation, no similar incident has been
reported and little data is available for comparisons, Japan's
atomic regulator, the Nuclear and Industrial Safety Agency,
Should Chubu Electric find serious damage inside the reactor
pressure vessel after the fuel rods are removed, the damage may
be irreparable, despite efforts to wash out the saltwater.
At a minimum, corrosion deposits may have formed a hard
scale on the fuel rods, making them unusable, said Toyoshi
Fuketa, deputy director general of the Japan Atomic Energy
Agency, who is on a regulatory panel examining Chubu Electric's
"They have to think hard about what they are going to do,"
Fuketa told Reuters.
The panel's experts have focused on whether below-par
welding could have accelerated metal fatigue in the pipe that
burst or if the structure of the heat exchanger was to blame.
Chubu Electric said on Monday completion of the plant's
tsunami defences, including a 1.6 km seawall on a raised
embankment 18 meters above sea level at a cost of 1 4 0 billion
yen ($1.79 billion), w i l l take one year longer than planned and
won't be finished until next December.
For the April-June quarter, Chubu said it had a net loss of
12.54 billion yen because of extra fuel and maintenance costs to
run fossil fuel plants.
The company has not estimated the cost of repairs to the
No.5 unit. There were no problems with the station's No.3 and
No.4 units during the shutdown last year. In 2008 the company
decided to decommission the No.1 and No.2 units about 10 years
earlier than planned because of higher costs to meet tougher
earthquake standards introduced in 2006.
The company will next meet the regulator's panel on Aug 10
and aims to end its investigation by the end of this year.
($1=78.2400 Japanese yen)
(Reporting by Risa Maeda; Editing by Aaron Sheldrick and